The present invention concerns a device for energy transmission for mechanical control, in particular for the control of braking pressure in a brake.
It applies in particular to hydraulic actuators which require very short response times and low production costs. Such devices are used in braking systems, power-assisted steering or automatic guiding of mobile mechanisms or vehicles, for example.
There are several solutions for energy transmission for mechanical control, in particular based on pneumatic, hydraulic or electrical devices. The response times of pneumatic devices are too long for many applications and electrical devices require large amounts of electrical energy which is incompatible with on-board systems. Moreover, these two types of devices are relatively expensive. Control systems in modern vehicles, in particular applied to braking or automatic guiding for example, require ever shorter response times, corresponding for example to pass-bands of approximately 10Hz. Furthermore, the reduction in the overall cost of vehicles or mechanisms means that the cost of their component parts, including those of the said control systems, must be further reduced. At the present time, only hydraulic devices seem likely to be the most suitable for transmitting energy for on-board mechanical control in mobile equipment or vehicles,sufficiently cheaply and quickly, in order to meet the requirements of new technical and economic conditions.
Devices generally used in the field of hydraulic control make use of complete systems such as servomechanisms based on flow or pressure valves, for example. Hydraulic devices have characteristics and architectures forming a homogeneous set and whose function of control of flow or pressure is achieved by several stages consisting of slide valves and springs.
Normally, these servomechanisms have two stages. The first stage is a linear actuator with a blade fitted with a shaft or a bar moving by magnetization which results from the action of a current flowing in a solenoid located near the bar. The second stage is a hydraulic amplifier consisting of a slide valve and a return spring, for example. Mechanical inertia, resonances and time constants complicate the action and limit the speed of movement of the parts. It is nevertheless possible to improve the performance of these systems, in particular the performance relating to their response time or pass-band, but with the disadvantage of greater complexity, and therefore production costs, which might be acceptable in aeronautical applications but not in terrestrial vehicles, for example, which are mass produced and whose cost must be low.
One known solution capable of overcoming these disadvantages, in particular, by simplifying the servo-action thanks to limitation of resonance and instability phenomena, consists in replacing the previous actuator, of linear type, by a rotational actuator, transmitting, via a connecting rod for example, a translational movement to the hydraulic slide valve and in replacing the spring of the second stage with a return spring acting on the rotational actuator. Although this last solution, albeit less complex and cheaper, does improve performance by avoiding resonance phenomena in particular, the desired response times, of the order of 0.1 second for example, corresponding to pass-bands of approximately 10 Hz, have yet not been achieved in the tests carried out so far.